U.S. patent application number 10/682075 was filed with the patent office on 2004-04-22 for optical signal processor.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Katayama, Makoto, Sano, Tomomi, Shigehara, Masakazu, Takushima, Michiko.
Application Number | 20040076368 10/682075 |
Document ID | / |
Family ID | 32096710 |
Filed Date | 2004-04-22 |
United States Patent
Application |
20040076368 |
Kind Code |
A1 |
Takushima, Michiko ; et
al. |
April 22, 2004 |
Optical signal processor
Abstract
An optical signal processor comprises optical input/output
means, a first optical system, wavelength branching means, a second
optical system, and reflecting means. The optical input/output
means includes a plurality of input/output ports. The ports have
respective light input/output directions, in parallel with each
other, located on a first virtual plane. The optical input/output
means inputs light into any of the ports and outputs the light from
any of the ports. The first optical system collimates the light.
The wavelength branching means spatially separates the light in
terms of wavelength, and outputs thus obtained wavelength light
components. The wavelength light components have respective optical
axes located on a second virtual plane. The second optical system
receives the wavelength light components and converges them. The
reflecting means includes a mirror with a reflecting surface
positioned at a light-converging point of the wavelength light
components converged by the second optical system. The reflecting
means causes the light reflected by the mirror to be outputted from
any of the ports. The first and second virtual planes are not
parallel to each other. The light fed into the wavelength branching
means has a greater beam width in a direction parallel to the
second virtual plane than in a direction perpendicular to the
second virtual plane.
Inventors: |
Takushima, Michiko;
(Yokohama-shi, JP) ; Sano, Tomomi; (Yokohama-shi,
JP) ; Katayama, Makoto; (Yokohama-shi, JP) ;
Shigehara, Masakazu; (Yokohama-shi, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
Sumitomo Electric Industries,
Ltd.
|
Family ID: |
32096710 |
Appl. No.: |
10/682075 |
Filed: |
October 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60462713 |
Apr 15, 2003 |
|
|
|
Current U.S.
Class: |
385/18 |
Current CPC
Class: |
G02B 6/272 20130101;
G02B 6/352 20130101; G02B 6/357 20130101; G02B 6/3518 20130101;
G02B 6/356 20130101; G02B 6/29311 20130101; G02B 6/2938 20130101;
G02B 6/29313 20130101 |
Class at
Publication: |
385/018 |
International
Class: |
G02B 006/26; G02B
006/42 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2002 |
JP |
P2002-297625 |
Claims
What is claimed is:
1. An optical signal processor comprising: optical input/output
means including a plurality of input/output ports for inputting or
outputting light; the plurality of input/output ports having
respective light input/output directions, in parallel with each
other, located on a first virtual plane; the optical input/output
means inputting light into any of the plurality of input/output
ports and outputting the light from any of the other input/output
ports; a first optical system for collimating the light arriving
from any of the plurality of input/output ports, and outputting
thus collimated light; wavelength branching means for receiving the
light collimated by the first optical system, spatially separating
the light in terms of wavelength, and outputting thus obtained
wavelength light components, thus outputted wavelength light
components having respective optical axes located on a second
virtual plane; a second optical system for receiving the wavelength
light components outputted from the wavelength branching means
after wavelength separation, and converging the wavelength light
components; and reflecting means including a mirror with a
reflecting surface positioned at a light-converging point of the
wavelength light components converged by the second optical system;
the reflecting means causing the light reflected by the mirror to
be outputted from any of the plurality of input/output ports by way
of the second optical system, wavelength branching means, and first
optical system; wherein the first and second virtual planes are not
parallel to each other; and wherein the light fed into the
wavelength branching means after being collimated by the first
optical system has a greater beam width in a direction parallel to
the second virtual plane than in a direction perpendicular to the
second virtual plane.
2. An optical signal processor according to claim 1, wherein the
wavelength branching means includes a diffraction grating
device.
3. An optical signal processor according to claim 1, wherein the
first and second virtual planes are perpendicular to each
other.
4. An optical signal processor according to claim 3, wherein a line
connecting a point where an optical axis of light fed from the
first optical system into the wavelength branching means intersects
the wavelength branching means and a point where an optical axis of
light fed from the second optical system into the wavelength
branching means intersects the wavelength branching means is
perpendicular to the second virtual plane.
5. An optical signal processor according to claim 4, wherein any
two mirrors included in the reflecting means have respective
inclination angles of reflecting surfaces different from each other
about a line, parallel to the second virtual plane and
perpendicular to an optical axis of the second optical system,
passing the light-converging point.
6. An optical signal processor according to claim 4, wherein each
mirror included in the reflecting means has a reflecting surface
with an inclination angle variable about a line, parallel to the
second virtual plane and perpendicular to an optical axis of the
second optical system, passing the light-converging point.
7. An optical signal processor according to claim 3, further
comprising: polarization separating means disposed between the
input/output means and the wavelength branching means; the
polarization separating means separating the light fed into any of
the plurality of input/output ports into respective polarized light
components having first and second directions orthogonal to each
other in terms of polarization, and outputting a first light beam
of the polarized light component having the first direction and a
second light beam of the polarized light component having the
second direction; and polarization plane rotating means disposed
between the polarization separating means and the wavelength
branching means; the polarization plane rotating means receiving
any of the first and second light beams outputted from the
polarization separating means, rotating a polarization direction of
the received light beam to make the first and second light beams
have the same polarization direction yielding the highest
wavelength branching efficiency in the wavelength branching means,
and outputting thus rotated light beam; wherein a line connecting a
point where an optical axis of the first light beam fed from the
first optical system into the wavelength branching means intersects
the wavelength branching means and a point where an optical axis of
the second light beam fed from the first optical system into the
wavelength branching means intersects the wavelength branching
means is parallel to the second virtual plane; and wherein a line
connecting a point where an optical axis of the first light beam
fed from the first optical system into the wavelength branching
means intersects the wavelength branching means and a point where
an optical axis of the second light beam fed from the second
optical system into the wavelength branching means intersects the
wavelength branching means is perpendicular to the second virtual
plane.
8. An optical signal processor according to claim 1, wherein
mirrors included in the reflecting means have respective reflecting
surfaces with the same inclination angle about a line,
perpendicular to the second virtual plane, passing the
light-converging point.
9. An optical signal processor according to claim 1, wherein each
mirror included in the reflecting means has a reflecting surface
with an inclination angle variable in N stages, whereas the optical
input/output means includes N+1 input/output ports (N being an
integer of 2 or greater).
10. An optical signal processor according to claim 1, wherein each
mirror included in the reflecting means has a reflecting surface
with an inclination angle variable in N stages, whereas the optical
input/output means includes 2N input/output ports (N being an
integer of 2 or greater).
11. An optical signal processor according to claim 10, wherein the
optical input/output means comprises a common input port, a common
output port, an n-th channel input port, and an n-th channel output
port as the 2N input/output ports; the n-th channel input port and
n-th channel output port inputting or outputting signal light in
the same channel; and wherein the number of input/output ports
located between the common input port and the n-th channel input
port is identical to the number of input/output ports located
between the common output port and the n-th channel output port,
where n=1 to N-1.
12. An optical signal processor according to claim 11, wherein the
common input port and the common output port are adjacent to each
other; and wherein the n-th channel input port and the n-th channel
output port are adjacent to each other.
13. An optical signal processor according to claim 1, wherein a
line of intersection between the reflecting surface of each mirror
included in the reflecting means and a plane, parallel to the
second virtual plane, including the light-converging point, is a
curve in an area including a center position of the
light-converging point.
14. An optical signal processor according to claim 13, wherein the
curve has a variable curvature.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Provisional Application
serial No. 60/462,713 filed on Apr. 15, 2003 which is hereby
incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical signal processor
which can multiplex or demultiplex multiwavelength signal
light.
[0004] 2. Related Background Art
[0005] Diffraction grating devices act as so-called wavelength
branching means. When multiplexed multiwavelength signal light is
inputted, a diffraction grating device can cause the
multiwavelength signal light to branch off spatially into the
individual wavelengths. An optical signal processor using such
wavelength branching means can receive multiplexed multiwavelength
signal light, demultiplex it into individual wavelengths or bands,
and output them; or multiplex multiwavelength signal light
components inputted for the individual wavelengths or bands and
output thus multiplexed signal light. The optical signal processor
is used as an optical multiplexer, an optical demultiplexer, an
optical ADM (Add Drop Multiplexer), and the like in optical
communication systems.
[0006] Such an optical signal processor is disclosed, for example,
in Document 1: U.S. Pat. No. 5,960,133. The optical signal
processor disclosed in Document 1 comprises a reflection type
diffraction grating device as wavelength branching means, a lens,
and mirrors. The diffraction grating device causes the light fed
into an input port to branch off spatially into individual
wavelengths. The lens converges the individual wavelength
components of signal light separated by the diffraction grating
device in terms of wavelength. The mirrors are disposed at
respective points on which the individual wavelength components of
signal light are converged by the lens. The individual wavelength
components of signal light reflected by the mirrors pass the lens
and diffraction grating device in the direction opposite from the
outgoing path, so as to be outputted from output ports. The mirrors
are provided for the individual wavelengths, whereas the angles of
inclination of their reflecting surfaces are controllable. By
adjusting the inclination angle of the reflecting surface of each
mirror, the optical signal processor acts as an optical ADM while
being able to change the wavelength of signal light to be added or
dropped.
SUMMARY OF THE INVENTION
[0007] The optical signal processor configured as mentioned above
has a structure in which wavelength components of signal light
after wavelength separation are converged onto reflecting surfaces
of mirrors by a lens. Therefore, in order to improve the wavelength
resolution, the degree of convergence is required to be high at the
time when the signal light is converged by the lens. In general,
for attaining a high degree of convergence, it will be sufficient
if the beam diameter of light is made greater when the light is
incident on the lens. However, in the optical signal processor
configured as mentioned above, it is necessary for the individual
wavelength components of signal light to be arranged parallel to
each other between the input/output port and the diffraction
grating device, so as to be kept from spatially overlapping each
other. Therefore, the optical signal processor must enhance its
size if its wavelength resolution is to be improved, whereby there
is a tradeoff between the improvement in wavelength resolution and
the smaller size.
[0008] In order to overcome the problem mentioned above, it is an
object of the present invention to provide an optical signal
processor which can improve its wavelength resolution and reduce
its size.
[0009] The optical signal processor in accordance with the present
invention comprises optical input/output means, a first optical
system, wavelength branching means, a second optical system, and
reflecting means. The optical input/output means includes a
plurality of input/output ports for inputting or outputting light.
The plurality of input/output ports have respective light
input/output directions, in parallel with each other, located on a
first virtual plane. The optical input/output means inputs light
into any of the plurality of input/output ports and outputs the
light from any of the other input/output ports. The first optical
system collimates the light arriving from any of the plurality of
input/output ports, and outputs thus collimated light. The
wavelength branching means receives the light collimated by the
first optical system, spatially separates the light in terms of
wavelength, and outputs thus obtained wavelength light components.
Thus outputted wavelength light components have respective optical
axes located on a second virtual plane. The second optical system
receives the wavelength light components outputted from the
wavelength branching means after wavelength separation, and
converges the wavelength light components. The reflecting means
includes a mirror with a reflecting surface positioned at a
light-converging point of the wavelength light components converged
by the second optical system. The reflecting means causes the light
reflected by the mirror to be outputted from any of the plurality
of input/output ports by way of the second optical system,
wavelength branching means, and first optical system. The first and
second virtual planes are not parallel to each other. The light fed
into the wavelength branching means after being collimated by the
first optical system has a greater beam width in a direction
parallel to the second virtual plane than in a direction
perpendicular to the second virtual plane.
[0010] The optical signal processor is operable as an optical
demultiplexer, an optical multiplexer, or an optical ADM. Namely,
when multiplexed signal light is fed into any of the plurality of
input/output ports included in the optical input/output means, the
multiplexed signal light is collimated by the first optical system
so as to be fed into the wavelength branching means, and is
spatially separated in terms of wavelength by the wavelength
branching means so as to be outputted into respective directions
corresponding to the individual wavelengths. The wavelength
components of signal light separated in terms of wavelength are
converged by the second optical system so as to be made incident on
and reflected by any mirror included in the reflecting means. Thus
reflected wavelength components of signal light are outputted from
any of the plurality of input/output ports after passing the second
optical system, wavelength branching means, and first optical
system. As such, the multiplexed signal light is demultiplexed.
When the light advances in the opposite direction, multiwavelength
signal light components are multiplexed, and thus multiplexed
signal light is outputted.
[0011] Here, the plurality of input/output ports included in the
optical input/output means have respective optical input/output
directions, in parallel with each other, located on the first
virtual plane. The wavelength components of light outputted from
the wavelength branching means after wavelength separation have
respective optical axes located on the second virtual plane. The
first and second virtual planes are not parallel to each other. The
light collimated by the first optical system so as to be fed into
the wavelength branching means has a greater beam width in a
direction parallel to the second virtual plane than in a direction
perpendicular to the second virtual plane. Such characteristic
features allow the optical signal processor to improve its
wavelength resolution and reduce its size.
[0012] Preferably, the wavelength branching means includes a
diffraction grating device. Preferably, the first and second
virtual planes are perpendicular to each other. Preferably, a line
connecting a point where an optical axis of light fed from the
first optical system into the wavelength branching means intersects
the wavelength branching means and a point where an optical axis of
light fed from the second optical system into the wavelength
branching means intersects the wavelength branching means is
perpendicular to the second virtual plane.
[0013] Preferably, any two mirrors included in the reflecting means
have respective inclination angles of reflecting surfaces different
from each other about a line, parallel to the second virtual plane
and perpendicular to an optical axis of the second optical system,
passing the light-converging point. Preferably, each mirror
included in the reflecting means has a reflecting surface with an
inclination angle variable about a line, parallel to the second
virtual plane and perpendicular to an optical axis of the second
optical system, passing the light-converging point.
[0014] Preferably, the optical signal processor further comprises
polarization separating means and polarization plane rotating
means. The polarization separating means is disposed between the
input/output means and the wavelength branching means. The
polarization separating means separates the light fed into any of
the plurality of input/output ports into respective polarized light
components having first and second directions orthogonal to each
other in terms of polarization, and outputs a first light beam of
the polarized light component having the first direction and a
second light beam of the polarized light component having the
second direction. The polarization plane rotating means is disposed
between the polarization separating means and the wavelength
branching means. The polarization plane rotating means receives any
of the first and second light beams outputted from the polarization
separating means, rotates a polarization direction of the received
light beam to make the first and second light beams have the same
polarization direction yielding the highest wavelength branching
efficiency in the wavelength branching means, and outputs thus
rotated light beam. Preferably, a line connecting a point where an
optical axis of the first light beam fed from the first optical
system into the wavelength branching means intersects the
wavelength branching means and a point where an optical axis of the
second light beam fed from the first optical system into the
wavelength branching means intersects the wavelength branching
means is parallel to the second virtual plane. Preferably, a line
connecting a point where an optical axis of the first light beam
fed from the first optical system into the wavelength branching
means intersects the wavelength branching means and a point where
an optical axis of the second light beam fed from the second
optical system into the wavelength branching means intersects the
wavelength branching means is perpendicular to the second virtual
plane. In this case, the loss upon demultiplexing or multiplexing
is low, and the polarization-dependent loss is small.
[0015] Preferably, mirrors included in the reflecting means have
respective reflecting surfaces with the same inclination angle
about a line, perpendicular to the second virtual plane, passing
the light-converging point.
[0016] Preferably, each mirror included in the reflecting means has
a reflecting surface with an inclination angle variable in N
stages, whereas the optical input/output means includes N+1
input/output ports (N being an integer of 2 or greater). This is
preferable for realizing an optical demultiplexer or optical
multiplexer.
[0017] Preferably, each mirror included in the reflecting means has
a reflecting surface with an inclination angle variable in N
stages, whereas the optical input/output means includes 2N
input/output ports (N being an integer of 2 or greater). This is
preferable for realizing an optical ADM.
[0018] Preferably, the optical input/output means comprises a
common input port, a common output port, an n-th channel input
port, and an n-th channel output port. Preferably, the n-th channel
input port and n-th channel output port input or output signal
light in the same channel. Preferably, the number of input/output
ports located between the common input port and the n-th channel
input port is identical to the number of input/output ports located
between the common output port and the n-th channel output
port.
[0019] Preferably, in the optical signal processor in accordance
with the present invention, the common input port and the common
output port are adjacent to each other, whereas the n-th channel
input port and the n-th channel output port are adjacent to each
other.
[0020] Preferably, in the optical signal processor in accordance
with the present invention, a line of intersection between the
reflecting surface of each mirror included in the reflecting means
and a plane, parallel to the second virtual plane, including the
light-converging point, is a curve in an area including a center
position of the light-converging point. Preferably, the curve has a
variable curvature.
[0021] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings. They are given by way of illustration only, and thus
should not be considered limitative of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIGS. 1A and 1B are schematic diagrams of the optical signal
processor in accordance with a first embodiment;
[0023] FIG. 2 is a sectional view of a MEMS substrate, mounted on a
platform, realizing a mirror;
[0024] FIG. 3 is a schematic diagram of the optical signal
processor in accordance with a second embodiment;
[0025] FIGS. 4A and 4B are schematic diagrams of the optical signal
processor in accordance with a third embodiment;
[0026] FIG. 5 is a schematic diagram of the optical signal
processor in accordance with a fourth embodiment; and
[0027] FIGS. 6A and 6B are explanatory views of a mirror having a
reflecting surface with a variable curved surface form.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] In the following, embodiments of the present invention will
be explained in detail with reference to the accompanying drawings.
In the explanation of the drawings, constituents identical to each
other will be referred to with numerals identical to each other
without repeating their overlapping descriptions. For convenience
of explanation, an xyz orthogonal coordinate system is shown in
each drawing. The y axis in the xyz orthogonal coordinate system is
parallel to the optical axis of a first optical system disposed
between an input/output port and a diffraction grating device. The
y axis is parallel to the optical axis of a second optical system
disposed between the diffraction grating device and a mirror. The z
axis in the xyz orthogonal coordinate system is common in the first
and second optical systems.
[0029] To begin with, the first embodiment of the optical signal
processor in accordance with the present invention will be
explained. FIG. 1A is a view of the optical signal processor 1 as
seen in a direction parallel to the z axis. FIG. 1B is a view of
the optical signal processor 1 as seen in a direction parallel to
the x axis. The optical signal processor 1 shown in these drawings
comprises input/output ports 111 to 114, lenses 121, 122, a
diffraction grating device 130, lenses 141, 142, and mirrors 151 to
153.
[0030] Each of the input/output ports 111 to 114 constitutes
optical input/output means for inputting or outputting light into
or from the optical signal processor 1. The input/output ports 111
to 114 have respective light input/output directions, located on a
first virtual plane (a plane parallel to the yz plane), parallel to
each other. Namely, when any of the input/output ports 111 to 114
is used for inputting, the optical axis of light directed from this
input/output port to the lens 121 is parallel to the y axis. When
any of the input/output ports 111 to 114 is used for outputting,
the optical axis of light directed from the lens 121 to the
input/output port is parallel to the y axis. The respective optical
axes of light beams between the input/output ports 111 to 114 and
the lens 121 are located on the first virtual plane. Preferably,
each of the input/output ports 111 to 114 is an optical fiber
collimator in which an end face of an optical fiber has a lens
function.
[0031] The lenses 121, 122 constitute a first optical system for
collimating light arriving from any of the input/output ports 111
to 114, and outputting thus collimated light to the diffraction
grating device 130. Each of the lenses 121, 122 is a cylindrical
lens, and exhibits a light-converging effect only in directions
parallel to the y axis. The lens 122 on the downstream stage
(farther from the input/output port) has a focal length longer than
that of the lens 121 on the upstream stage (closer to the
input/output port). The gap between the lenses 121, 122 is set
equal to the sum of their focal lengths. As a consequence, the
light outputted from the first optical system comprising the lenses
121, 122 after collimation attains a greater beam width in a
direction parallel to the x axis than in a direction parallel to
the z axis.
[0032] The diffraction grating device 130 acting as wavelength
branching means is of transmission type. The diffraction grating
device 130 inputs the light arriving after being collimated by the
first optical system, and diffracts individual wavelength
components included in thus inputted light at respective
diffraction angles corresponding to the wavelengths, so as to
separate the wavelength light components spatially in terms of
wavelength and output them to the lens 141. The diffraction grating
device 130 is arranged such that its grating direction is parallel
to the z axis. Therefore, when the optical axis of light incident
on the diffraction grating device 130 is parallel to the y axis,
the optical axes of wavelength light components outputted from the
diffraction grating device 130 after wavelength separation are
located on a second virtual plane (a plane parallel to the xy
plane).
[0033] The lenses 141, 142 constitute a second optical system for
converging the individual wavelength light components outputted
from the diffraction grating device 130 after wavelength
separation. Each of the lenses 141, 142 is a cylindrical lens. The
lens 141 on the upstream side exhibits a light-converging effect
only in directions parallel to the x axis. The lens 142 on the
downstream side exhibits a light-converging effect only in
directions parallel to the z axis. Light-converging points formed
by the lenses 141, 142 are located on reflecting surfaces of the
mirrors 151 to 153. As a consequence, the light converged by the
second optical system comprising the lenses 141, 142 is focused
onto the reflecting surfaces of the mirrors 151 to 153. If the
lenses 141, 142 have no chromatic aberration, the light-converging
points of individual wavelength light components exist on a line
parallel to the x axis.
[0034] The mirrors 151 to 153 constitute reflecting means having
respective reflecting surfaces at the light-converging points of
individual wavelength light components converged by the second
optical system, and reflecting the wavelength light components at
the reflecting surfaces. Each of the mirrors 151 to 153 has a
reflecting surface whose inclination angle is appropriately set. As
a consequence, the individual wavelength light components reflected
by the reflecting surfaces are outputted from any of the
input/output ports 111 to 114 by way of the second optical system
(lenses 142, 141), diffraction grating device 130, and first
optical system (lenses 122, 121).
[0035] The first and second virtual planes are not parallel to each
other but perpendicular to each other in this embodiment in
particular. The light fed into the diffraction grating device 130
after being collimated by the first optical system has a greater
beam width in a direction parallel to the second virtual plane (a
direction parallel to the x axis) than in a direction perpendicular
to the second virtual plane (a direction parallel to the z
axis).
[0036] A line connecting a point where the optical axis of light
fed from the first optical system into the diffraction grating
device 130 intersects the diffraction grating device 130 and a
point where the optical axis of light fed from the second optical
system into the diffraction grating device 130 is parallel to the z
axis and perpendicular to the second virtual plane.
[0037] The mirrors 151 to 153 have respective reflecting surfaces
with the same inclination angle about a line (parallel to the z
axis), perpendicular to the second virtual plane, passing the
light-converging point. Preferably, any two of the mirrors 151 to
153 have reflecting surfaces with different inclination angles
about a line (parallel to the x axis), parallel to the second
virtual plane and perpendicular to the optical axis of the second
optical system, passing the light-converging point. The inclination
angle of the reflecting surface in each of the mirrors 151 to 153
may be fixed or variable. In the latter case, the inclination angle
of the reflecting surface in each of the mirrors 151 to 153 is
variable about a line (parallel to the x axis), parallel to the
second virtual plane and perpendicular to the optical axis of the
second optical system, passing the light-converging point.
[0038] In response to the four input/output ports provided, the
inclination angle of the reflecting surface in each of the mirrors
151 to 153 can be changed in three stages whose number is smaller
than the number of input/output ports by 1. Namely, the inclination
angle of the reflecting surface in each mirror is variable in N
stages, whereas N+1 input/output ports are provided in response
thereto. Here, N is an integer of 2 or greater in general, and 3 in
this embodiment. Thus configured optical signal processor 1 is
operable as an optical demultiplexer or optical multiplexer.
[0039] Operations of the optical system 1 in accordance with the
first embodiment will now be explained. In the following
explanation, it is assumed that three wavelength signal light
components .lambda..sub.1 to .lambda..sub.3 are multiplexed, and
that thus multiplexed signal light is fed into the input/output
port 111. Also, the mirrors 151 to 153 are assumed to reflect the
signal light components .lambda..sub.1 to .lambda..sub.3,
respectively.
[0040] The multiplexed signal light components .lambda..sub.1 to
.lambda..sub.3 fed from the input/output port 111 are collimated by
the first optical system constituted by the lenses 121, 122, so as
to be made incident on the diffraction grating device 130. Here,
because of the effect of the first optical system, the light
incident on the diffraction grating device 130 enhances its beam
width only in a direction parallel to the second virtual plane (a
direction parallel to the x axis). The multiplexed signal light
components .lambda..sub.1 to .lambda..sub.3 incident on the
diffraction grating device 130 from the first optical system are
diffracted by the diffraction grating device 130 at respective
diffraction angles corresponding to the wavelengths, so as to be
spatially separated in terms of wavelength. The multiplexed signal
light components .lambda..sub.1 to .lambda..sub.3 separated in
terms of wavelength by the diffraction grating device 130 are
converged within a plane parallel to the xy plane by the lens 141,
and are converged within a plane parallel to the yz plane by the
lens 142, so as to be focused onto the reflecting surface in any of
the mirrors 151 to 153.
[0041] The signal light component .lambda..sub.1 collected by the
second optical system is reflected by the mirror 151 having a
reflecting surface at the light-converging point of signal light
component .lambda..sub.1. The signal light component .lambda..sub.1
diverges immediately after reflection. However, since the
inclination of the reflecting surface in the mirror 151 is set
appropriately, the signal light component .lambda..sub.1 is
collimated by the second optical system (lenses 142, 141),
diffracted by the diffraction grating device 130, and then
outputted from any of the input/output ports 111 to 114 with its
beam width reduced in a direction parallel to the second virtual
plane (a direction parallel to the x axis). In a similar manner,
the signal light components .lambda..sub.2 and .lambda..sub.3
converged by the second optical system are processed. The signal
light component .lambda..sub.2 reflected by the mirror 152 is
outputted from any of the input/output ports 111 to 114. The signal
light component .lambda..sub.3 reflected by the mirror 153 is
outputted from any of the input/output ports 111 to 114.
[0042] The respective projections of the outgoing path (optical
path directed from the input/output port to the mirror) and the
incoming path (optical path directed from the mirror to the
input/output port) onto the xy plane coincide with each other at
the same wavelength. Between the input/output ports 111 to 114 and
the lens 142, the signal light components .lambda..sub.1 to
.lambda..sub.3 also advance in parallel with the y axis on the
first virtual plane (plane parallel to the yz plane) in the
incoming path as in the outgoing path.
[0043] Which input/output ports the signal light components
.lambda..sub.1 to .lambda..sub.3 reach after traveling the incoming
path is determined by the inclination angle of the reflecting
surface in each of the mirrors 151 to 153. For example, the signal
light components .lambda..sub.1 to .lambda..sub.3 having traveled
the incoming path can reach the input/output ports 112, 113, 114,
respectively. In this case, the optical signal processor 1 operates
as an optical demultiplexer for demultiplexing the inputted
multiplexed signal light components .lambda..sub.1 to
.lambda..sub.3 into the individual wavelengths, and outputting thus
demultiplexed wavelength components. When the signal light
components .lambda..sub.1 to .lambda..sub.3 are fed into the input
ports 112, 113, 114, respectively, these signal light components
travel the opposite optical paths, so as to be outputted from the
input/output port 111 after being multiplexed. In this case, the
optical signal processor 1 operates as an optical multiplexer for
multiplexing the individually inputted signal light components
.lambda..sub.1 to .lambda..sub.3, and outputting thus multiplexed
signal light.
[0044] Also, for example, the signal light components
.lambda..sub.1 and .lambda..sub.2 having traveled the incoming path
can reach the input/output port 113 whereas the signal light
component .lambda..sub.3 having traveled the incoming path can
reach the input/output port 114. When the signal light components
.lambda..sub.1 and .lambda..sub.2 reach the input/output port 113
whereas the signal light component .lambda..sub.3 reaches the
input/output port 114, these signal light components travel their
opposite paths, so as to be outputted from the input/output port
111 after being multiplexed. The optical signal processor 1 also
operates as an optical demultiplexer or optical multiplexer for
demultiplexing or multiplexing the signal light components
.lambda..sub.1 to .lambda..sub.3 in these cases.
[0045] In the light incident on the diffraction grating device 130
from the first optical system, the beam width in a direction
parallel to the x axis is enlarged by the first optical system in
this embodiment. Therefore, the light-converging point of each
wavelength component of signal light converged by the second
optical system after being outputted from the diffraction grating
device 130 is sharp and has a small size. The optical signal
processor 1 in accordance with this embodiment has such a high
degree of convergence, and thus attains a high wavelength
resolution. Though the beam width of light incident on the
diffraction grating device 130 is enlarged in one direction, the
light-converging point can be made smaller in the reflecting
surface of each of the mirrors 151 to 153, whereas the beam
diameter can be made smaller at the time of inputting or outputting
light in each of the input/output ports 111 to 114. Therefore, the
optical signal processor 1 in accordance with this embodiment can
be made smaller.
[0046] As mentioned above, the inclination angle of the reflecting
surface in each of the mirrors 151 to 153 is preferably variable.
Such mirrors 151 to 153 can be made smaller by using the MEMS
(Micro Electro Mechanical System) technology. For example, it is
possible to realize one having a size of several tens of
micrometers, which can be driven two-dimensionally. When using the
MEMS technology, a mirror is realized in the following manner.
[0047] First, a pattern is formed by photolithography with a
submicron precision on a substrate made of Si or SOI, and a
desirable structure is formed by reactive etching. After the
formation, a plurality of structures are bonded together in the
case of the Si substrate. In the case of the SOI substrate, the
structure is made movable after a sacrifice layer removing process,
whereby a driver for driving a mirror is formed. Signal light
generally employed in optical communications falls within an
infrared region, whereas Si is transparent to infrared light.
Therefore, a mirror comprises a base made of chromium and a coating
layer of gold formed thereon. Here, in order for the gold coating
layer to sufficiently block the light in a wavelength region
generally used in optical communications, the gold coating layer
preferably has a thickness of about 0.1 .mu.m or greater. Examples
of mechanism for driving a mirror include those using a hinge and a
thin spring-like member. Such a driving mechanism realizes a mirror
adapted to adjust the inclination angle by several degrees on a
flat substrate.
[0048] It is necessary to assemble a structure in which a plurality
of mirrors are arranged as with the mirrors 151 to 153 included in
the optical signal processor 1 in accordance with this embodiment.
MEMS chips are often subjected to dicing in general, which may be
problematic in terms of the perpendicularity of cross sections and
the accuracy in cut positions. Preferably, the anisotropy of Si
crystals is utilized, so as to form vertical planes by wet etching.
It will also be preferred if vertical planes are formed by deep
reactive ion etching.
[0049] In another preferable mirror arranging structure, a platform
mounting the wavelength branching means and a platform mounting a
MEMS substrate are arranged in parallel with each other. FIG. 2 is
a sectional view of a structure in which a MEMS substrate realizing
a mirror is mounted on a platform. As shown in this sectional view,
a mirror 902 is realized on one surface of a MEMS substrate 901.
The other surface of the MEMS substrate 901 is secured onto a
surface of a flat platform 903. A mirror 904 is disposed above the
mirror 902. The mirror 902 corresponds to the mirrors 151 to 153 in
FIGS. 1A and 1B, whereas a normal of its reflecting surface is
parallel to the z axis. The mirror 904 inputs light incident
thereon in parallel with the y axis from the second optical system,
and reflects the light into a direction parallel to the z axis, so
as to output the reflected light toward the mirror 902. The mirror
904 maybe realized by a prism as well. In such a configuration, the
MEMS substrate 901 and platform 903 theoretically have quite
favorable thicknesses and parallelism, whereby there is no need to
take account of the alignment accuracy in directions parallel to
the z axis. Also, the mirror (or prism) 904 can easily be formed by
using LIGA (Lithographic Galvanoforming Abforming; lithography
utilizing synchrotron orbital radiation).
[0050] A second embodiment of the optical signal processor in
accordance with the present invention will now be explained. FIG. 3
is a schematic diagram of the optical signal processor 2 in
accordance with the second embodiment. This diagram shows the
optical signal processor 2 as seen in a direction parallel to the z
axis. The diagram of the optical signal processor 2 as seen in a
direction parallel to the x axis is substantially the same as FIG.
1B and thus is omitted.
[0051] The optical signal processor 2 shown in FIG. 3 comprises
input/output ports 211 to 214, lenses 221, 222, a diffraction
grating device 230, lenses 241, 242, and mirrors 251 to 253. These
constituents are equivalent to those included in the optical signal
processor 1 in accordance with the first embodiment shown in FIGS.
1A and 1B. For simplification, this diagram shows only the mirror
251 among the mirrors 251 to 253, and only the optical path of
signal light converged onto the reflecting surface of the mirror
251.
[0052] The optical signal processor 2 in accordance with the second
embodiment further comprises a polarization beam splitter 261, a
mirror 262, and a half-wave plate 263 which are disposed between
the input/output ports 211 to 214 and the lens 221.
[0053] The polarization beam splitter 261 acts as polarization
separating means. Namely, the polarization beam splitter 261
receives light from any of the input/output ports 211 to 214, and
separates the light in terms of polarization into respective
polarized light components having first and second directions
orthogonal to each other. Then, the polarization beam splitter 261
outputs a first light beam of the polarized light component having
the first direction into the first optical path P.sub.1, and a
second light beam of the polarized light component having the
second direction into the second optical path P.sub.2. The first
direction is a polarization direction yielding the highest
diffraction efficiency in the diffraction grating device 230. The
second direction is a polarization direction orthogonal to the
first direction. Immediately after the first light beam is
outputted from the polarization beam splitter 261, the first
optical path P.sub.1 is parallel to the y axis. Immediately after
the second light beam is outputted from the polarization beam
splitter 261, the second optical path P.sub.2 is parallel to the x
axis.
[0054] The mirror 262 is disposed on the second optical path
P.sub.2 between the polarization beam splitter 261 and the lens
221. The mirror 262 reflects the second light beam outputted into
the second optical path P.sub.2 from the polarization beam splitter
261, and outputs thus reflected second light beam into a direction
parallel to the y axis. The half-wave plate 263 acts as
polarization plane rotating means. Namely, the half-wave plate 263
is disposed on the second optical path P.sub.2 between the mirror
262 and the lens 221. The half-wave plate 263 receives the second
light beam outputted to the second optical path P.sub.2 from the
mirror 262, rotates the polarization direction of the second light
beam by 90.degree. so as to attain the first polarization
direction, and outputs the second light beam having the first
polarization direction into the second optical path P.sub.2.
[0055] The first light beam outputted from the polarization beam
splitter 261 to the first optical path P1 is immediately collimated
by the first optical system (lenses 221, 222), so as to be fed into
the diffraction grating device 230 in a direction parallel to the y
axis. In the second light beam outputted from the polarization beam
splitter 261 to the second optical path P.sub.2, the polarization
direction is rotated by 90.degree. by the half-wave plate 263.
Then, the second light beam is collimated by the first optical
system (lenses 221, 222), so as to be fed into the diffraction
grating device 230 in a direction parallel to the y axis. Thus,
each of the first and second light beams fed from the first optical
system (lenses 221, 222) to the diffraction grating device 230 has
the first polarization direction. Therefore, the first and second
light beams are diffracted at a high efficiency by the diffraction
grating device 230.
[0056] As in the first embodiment, the respective optical
input/output directions of the input/output ports 211 to 214 are
located on the first virtual plane (plane parallel to the yz plane)
and are parallel to each other in the second embodiment. The
individual wavelength light components (in both the first optical
path P.sub.1 and second optical path P.sub.2) outputted from the
diffraction grating device 230 after wavelength separation have
respective optical axes located on the second virtual plane (plane
parallel to the xy plane). The first and second virtual planes are
perpendicular to each other. The light incident on the diffraction
grating device 230 after being collimated by the first optical
system (in both the first optical path P.sub.1 and second optical
path P.sub.2) has a greater beam width in a direction parallel to
the second virtual plane (a direction parallel to the x axis) than
the beam width in a direction perpendicular to the second virtual
plane (a direction parallel to the z axis).
[0057] In the second embodiment, a line connecting a point where
the optical axis of the first light beam (optical axis of the first
optical path P.sub.1) fed from the first optical system into the
diffraction grating device 230 intersects the diffraction grating
device 230 and a point where the optical axis of the second light
beam (optical axis of the second optical path P.sub.2) fed from the
first optical system into the diffraction grating device 230
intersects the diffraction grating device 230 is parallel to the
second virtual plane (plane parallel to the xy plane).
[0058] In the second embodiment, the first and second light beams
fed from the first optical system (lenses 221, 222) into the
diffraction grating device 230 are inputted to the diffraction
grating device 230 in a direction parallel to the y axis and are
diffracted at the same diffraction angle by the diffraction grating
device 230. Thus diffracted first and second light beams advance in
parallel with each other from the diffraction grating device 230
toward the lens 241, and are converged at the same light-converging
point on the reflecting surface of the mirror 251.
[0059] The first and second light beams diverge immediately after
being reflected by the mirror 251, but are collimated by the second
optical system (lenses 242, 241) and are diffracted by the
diffraction grating device 230. Then, the beam width of each light
beam in a direction parallel to the second virtual plane (a
direction parallel to the x axis) is reduced by the first optical
system (lenses 222, 221). Thereafter, the first and second light
beams are combined in terms of polarization by the half-wave plate
263 and polarization beam splitter 261, and thus combined light is
outputted from any of the input/output ports 211 to 214.
[0060] In the second embodiment, a line connecting a point where
the optical axis of the first light beam fed from the first optical
system into the diffraction grating device 230 intersects the
diffraction grating device 230 in the outgoing path and a point
where the optical axis of the second light beam fed from the second
optical system into the diffraction grating device 230 intersects
the diffraction grating device 230 in the incoming path is parallel
to the z axis and perpendicular to the second virtual plane (plane
parallel to the xy plane). Namely, the projection of the outgoing
path of the first light beam onto the xy plane and the projection
of the incoming path of the second light beam onto the xy plane
coincide with each other. Also, the projection of the outgoing path
of the second light beam onto the xy plane and the projection of
the incoming path of the first light beam onto the xy plane
coincide with each other.
[0061] The second optical signal processor 2 in accordance with
this embodiment can exhibit the following effects in addition to
those obtained by the optical signal processor 1 in accordance with
the first embodiment. Namely, since the second embodiment comprises
the polarization beam splitter 261, mirror 262, and half-wave plate
263, the light incident on the diffraction grating device 230
always attains a polarization direction yielding the highest
diffraction efficiency in the diffraction grating device 230. As a
consequence, regardless of the polarization state of input light,
the optical signal processor 2 yields a low loss at the time of
demultiplexing or multiplexing, and a small polarization-dependent
loss.
[0062] The reflecting surface of the mirror 251 has a variable
inclination angle about a line (parallel to the x axis), parallel
to the second virtual plane and perpendicular to the optical axis
of the second optical system, passing the light-converging point.
The same holds in the mirrors 252, 253. The mirrors 251 to 253 have
respective reflecting surfaces having the same inclination angle
about a line (parallel to the z axis), perpendicular to the second
virtual plane, passing the light-converging point. For setting the
inclination angle of the reflecting surface in each of the mirrors
251 to 253 as such, the respective optical axes of individual
wavelength components of signal light are required to be parallel
to each other from the lens 241 to each of the mirrors 251 to
253.
[0063] When the lens 241 is a thin lens, for example, the angle
formed between the optical axis of light incident on the mirror 241
and the yz plane is represented by the following expression:
(1-L/f)tan(.beta..sub.0-.beta.)-x.sub.0/f (1)
[0064] Here, .lambda. is represented by the following
expression:
.lambda.=.LAMBDA.(sin .beta..sub.in-sin .beta.) (2)
[0065] Here, L is the distance along the optical path from the
diffraction grating device 230 to the lens 241. f is the focal
length of the lens 241. A is the grating period of the diffraction
grating device 230. .beta..sub.in is the incident angle of light
onto the diffraction grating device 230. .beta. is the diffraction
angle of light having the wavelength .lambda. in the diffraction
grating device 230. .beta..sub.0 is the diffraction angle of light
having a specific wavelength diffracted into a direction parallel
to the optical axis of the lens 241. x.sub.0 is the x-coordinate
value of light having the above-mentioned specific wavelength on
the lens 231 when the x-coordinate value of the center point of the
lens 231 is taken as 0.
[0066] In order for the respective optical axes of individual
wavelength components of signal light to become parallel to each
other from the lens 241 to each of the mirrors 251 to 253, the
incident angle represented by the above-mentioned expression (1) is
independent from the wavelength .lambda.. Namely, it will be
sufficient if the relational expression:
f=L (3)
[0067] holds. The second optical system can attain a configuration
satisfying the relationship of the above-mentioned expression (3)
even when having a complicated structure including a plurality of
lenses.
[0068] A third embodiment of the optical signal processor in
accordance with the present invention will now be explained. FIGS.
4A and 4B are schematic diagrams of the optical signal processor 3
in accordance with the third embodiment. FIG. 4A is a diagram of
the optical signal processor 3 as seen in a direction parallel to
the z axis. FIG. 4B is a diagram of the optical signal processor 3
as seen in a direction parallel to the x axis.
[0069] The optical signal processor 3 shown in these diagrams
comprises input/output ports 311 to 318, a first optical system
320, a diffraction grating device 330, lenses 341, 342, and mirrors
351 to 355. Though the first optical system 320 in this embodiment
preferably has a configuration in which two cylindrical lenses are
combined together as in each of the first and second embodiments,
the configuration is depicted in a simplified form here.
[0070] The individual constituents included in the optical signal
processor 3 shown in these diagrams are equivalent to those
included in the optical signal processor 1 in accordance with the
first embodiment shown in FIGS. 1A and 1B except for particulars
concerning numbers thereof, and are arranged similarly to the
optical signal processor 1. Therefore, operations and effects of
the optical signal processor 3 are substantially the same as those
of the optical signal processor 1 in accordance with the first
embodiment.
[0071] Namely, as in the first embodiment, the input/output ports
311 to 318 have respective light input/output directions, located
on the first virtual plane (plane parallel to the yz plane),
parallel to each other. The individual wavelength light components
outputted from the diffraction grating device 330 after wavelength
separation have respective optical axes located on the second
virtual plane (plane parallel to the xy plane). The first and
second virtual planes are perpendicular to each other. The light
incident on the diffraction grating device 330 after being
collimated by the first optical system 320 has a greater beam width
in a direction parallel to the second virtual plane (a direction
parallel to the x axis) than in a direction perpendicular to the
second virtual plane (a direction parallel to the z axis). Such a
configuration allows the optical signal processor 3 in accordance
with this embodiment to yield a high wavelength resolution and
reduce its size.
[0072] The optical signal processor 3 in accordance with this
embodiment comprises five mirrors 351 to 355 in response to eight
input/output ports 311 to 318. The inclination angle of the
reflecting surface in each of the mirrors 351 to 355 is changeable
in four stages. Namely, the inclination angle of the reflecting
surface in each mirror is changeable in N stages, and 2N
input/output ports are provided in response thereto. Here, N is an
integer of 3 or greater in general, and 4 in this embodiment. Thus
configured optical signal processor 3 is operable not only as an
optical demultiplexer or optical multiplexer, but also as an
optical ADM. In the following, a case where the optical signal
processor 3 operates as an optical ADM will be explained.
[0073] The eight input/output ports 311 to 318 are arranged in this
order in a direction parallel to the z axis. It is assumed that the
input/output port 313 is a common input port for inputting
multiplexed signal light components .lambda..sub.1 to
.lambda..sub.5, and that the input/output port 314 is a common
output port for outputting multiplexed signal light components
.lambda..sub.1 to .lambda..sub.5. It is also assumed that the five
wavelength signal light components .lambda..sub.1 to .lambda..sub.5
are reflected by the mirrors 351 to 355, respectively.
[0074] The remaining six input/output ports 311, 312, 315 to 318
are ports for adding or dropping any of the five wavelength signal
light components .lambda..sub.1 to .lambda..sub.5. In particular,
each of the input/output ports 311, 315, 317 is an input port for
adding the signal light, whereas each of the input/output ports
312, 316, 318 is an output port for dropping the signal light. The
respective inclination angles of the reflecting surfaces in the
mirrors 351 to 355 are set appropriately according to which
input/output ports are to be used for adding or dropping.
[0075] The multiplexed signal light components .lambda..sub.1 to
.lambda..sub.5 fed from the common input port 313 are collimated by
the first optical system 320, so as to be made incident on the
diffraction grating device 330. Here, because of the effect of the
first optical system 320, the light incident on the diffraction
grating device 330 enhances its beam width only in a direction
parallel to the second virtual plane (a direction parallel to the x
axis). The multiplexed signal light components .lambda..sub.1 to
.lambda..sub.5 incident on the diffraction grating device 330 from
the first optical system 320 are diffracted by the diffraction
grating device 330 at respective diffraction angles corresponding
to the wavelengths, so as to be separated spatially in terms of
wavelength. The signal light components .lambda..sub.1 to
.lambda..sub.5 separated in terms of wavelength by the diffraction
grating device 330 are converged within a plane parallel to the xy
plane by the lens 341, and are converged within a plane parallel to
the yz plane by the lens 342, so as to be converged onto any of the
reflecting surfaces of the mirrors 351 to 355.
[0076] The signal light component .lambda..sub.1 converged by the
second optical system is reflected by the mirror 351 whose
reflecting surface is located at the light-converging point of the
signal light component .lambda..sub.1. The inclination of the
reflecting surface of the mirror 351 is set appropriately.
Therefore, though diverging immediately after being reflected, the
signal light component .lambda..sub.1 reflected by the mirror 351
is collimated by the second optical system (lenses 342, 341) and
then diffracted by the diffraction grating device 330. Thereafter,
with the beam width reduced in a direction parallel to the second
virtual plane (a direction parallel to the x axis) by the first
optical system 320, the signal light component .lambda..sub.1 is
outputted from any of the common output port 314 and the output
ports 312, 316, and 318. The signal light components .lambda..sub.2
to .lambda..sub.5 converged by the second optical system are
processed similarly, so that the signal light components
.lambda..sub.2 to .lambda..sub.5 reflected by the mirrors 352 to
355 are outputted from any of the common output port 314 and the
output ports 312, 316, and 318.
[0077] For example, in the multiplexed signal light components
.lambda..sub.1 to .lambda..sub.5 fed into the common input port
313, the signal light component .lambda..sub.1 is outputted from
the output port 318, the signal light component .lambda..sub.2 is
outputted from the output port 316, the signal light components
.lambda..sub.3, .lambda..sub.4 are outputted from the common output
port 314, and the signal light component .lambda..sub.2 is
outputted from the output port 312. Here, the signal light
components .lambda..sub.1, .lambda..sub.2, .lambda..sub.5 fed into
the input ports 317, 315, 311, respectively, are outputted from the
common output port 314 after being multiplexed with the signal
light components .lambda..sub.3, .lambda..sub.4 fed into the common
input port 313. By appropriately setting the inclination angle of
each of the reflecting surfaces of the mirrors 351 to 355, the
optical signal processor 3 in accordance with this embodiment can
set the signal light wavelengths and input/output port positions to
be added or dropped, and thus can operate as a three-channel
variable optical ADM.
[0078] When the optical signal processor 3 operates as an optical
ADM as such, it is necessary for the incident angle of light from
the common input port 313 and the reflection angle of the light
directed to the output port for dropping the signal light component
.lambda..sub.n to equal each other in the mirror for reflecting the
signal light component .lambda..sub.n. Also, in the mirror for
reflecting the signal light component .lambda..sub.n, it is
necessary for the incident angle of light from the input port for
adding the signal light component .lambda..sub.n and the reflection
angle of the light directed to the common output port 314 to equal
each other. To this aim, it is desirable that the number of
input/output ports located between the common input port 313 and
the input port for the signal light component .lambda..sub.n and
the number of input/output ports located between the common output
port 314 and the output port for the signal light component
.lambda..sub.n equal each other. Preferably, the common input port
313 and the common output port 314 are adjacent to each other,
whereas the input port for the signal light component
.lambda..sub.n and the output port for the signal light component
.lambda..sub.n are adjacent to each other. The input/output ports
311 to 318 satisfy such relationships in the explanation of
operations mentioned above.
[0079] A fourth embodiment of the optical signal processor in
accordance with the present invention will now be explained. FIG. 5
is a schematic diagram of the optical signal processor 4 in
accordance with the fourth embodiment. This diagram shows the
optical signal processor 4 as seen in a direction parallel to the z
axis. The diagram of the optical signal processor 4 as seen in a
direction parallel to the x axis is substantially the same as FIG.
1B and thus is omitted.
[0080] The optical signal processor 4 shown in FIG. 5 comprises
input/output ports 411 to 416, a first optical system 420, a
diffraction grating device 430, lenses 441, 442, and mirrors 451 to
455. Though the first optical system 420 in this embodiment
preferably has a configuration in which two cylindrical lenses are
combined together as in each of the first and second embodiments,
the configuration is depicted in a simplified form here.
[0081] The individual constituents included in the optical signal
processor 4 shown in these diagrams are equivalent to those
included in the optical signal processor 1 in accordance with the
first embodiment shown in FIGS. 1A and 1B except for particulars
concerning numbers thereof, and are arranged similarly to the
optical signal processor 1. Therefore, operations and effects of
the optical signal processor 4 are substantially the same as those
of the optical signal processor 1 in accordance with the first
embodiment.
[0082] Namely, as in the first embodiment, the input/output ports
411 to 416 have respective light input/output directions, located
on the first virtual plane (plane parallel to the yz plane),
parallel to each other. The individual wavelength light components
outputted from the diffraction grating device 430 after wavelength
separation have respective optical axes located on the second
virtual plane (plane parallel to the xy plane). The first and
second virtual planes are perpendicular to each other. The light
incident on the diffraction grating device 430 after being
collimated by the first optical system 420 has a greater beam width
in a direction parallel to the second virtual plane (a direction
parallel to the x axis) than in a direction perpendicular to the
second virtual plane (a direction parallel to the z axis). Such a
configuration allows the optical signal processor 3 in accordance
with this embodiment to yield a high wavelength resolution and
reduce its size.
[0083] The optical signal processor 4 in accordance with this
embodiment comprises five mirrors 451 to 455 in response to six
input/output ports 411 to 416. The inclination angle (the angle of
inclination about a line parallel to the x axis) of the reflecting
surface in each of the mirrors 451 to 455 is changeable in five
stages. Namely, the inclination angle of the reflecting surface in
each mirror is changeable in N stages, and N+1 input/output ports
are provided in response thereto. Here, N is an integer of 2 or
greater in general, and 5 in this embodiment. Thus configured
optical signal processor 4 is operable as an optical demultiplexer
or optical multiplexer, as in the first embodiment.
[0084] In particular, each of the reflecting surfaces of the
mirrors 451 to 455 is formed as a curved surface in the fourth
embodiment. Namely, in each of the mirrors 451 to 455, a line of
intersection between a plane (parallel to the xy plane), parallel
to the second virtual plane, including the light-converging point
and the reflecting surface is a curve in an area including the
center position of the light-converging point. Preferably, the
curve has a variable curvature.
[0085] Thus, each of the reflecting surfaces of the mirrors 451 to
455 is formed as a curved surface. Therefore, the optical signal
processor 4 in accordance with this embodiment can adjust the
chromatic dispersion when operating as an optical demultiplexer or
optical multiplexer. While signal light is incident on the
light-converging point on the reflecting surface in each of the
mirrors 451 to 455, the signal light has a certain degree of
wavelength expansion in general, so that the center wavelength
component of signal light is incident at the center position of the
light-converging point, whereas wavelength components distanced
from the center wavelength are incident at positions separated from
the center position. Since the reflecting surface is formed as a
curved surface, the signal incident on and reflected by the
reflecting surface incurs a group delay corresponding to the
wavelength, whereby the chromatic dispersion is adjusted. When the
curved surface form of the reflecting surface is variable, the
chromatic dispersion adjustment amount also becomes variable.
[0086] Such mirrors 451 to 455 can be realized in the following
manner. FIGS. 6A and 6B are explanatory views of a mirror having a
reflecting surface whose curved surface form is variable. FIG. 6A
is a schematic view showing the form and driving method of the
mirror, whereas FIG. 6B is a sectional view showing a specific
example. The reflecting means 910 shown in these drawings comprises
a single movable reflecting mirror 911. The movable reflecting
mirror 911 corresponds to the mirrors 451 to 455 in FIG. 5.
[0087] As shown in FIG. 6A, by deforming the curved surface form of
the whole reflecting surface (into a parabolic form, for example),
the movable reflecting mirror 911 can move respective reflecting
surface parts corresponding to individual frequency components of
signal light with respect to the signal light propagating
direction. This can accurately adjust dispersion in a variable
manner.
[0088] FIG. 6B shows a specific configurational example of the
reflecting means 910 having such a single movable reflecting mirror
911. In the reflecting means 910, a metal layer 911 to become a
movable reflecting mirror is formed on a polysilicon layer 912. The
metal layer 911 also functions as a first electrode provided with
the movable mirror.
[0089] A metal layer 914 formed on a silicon layer 915 is disposed
on the side of the polysilicon layer 912 opposite from the metal
layer 911. The metal layer 914 is a second electrode disposed at a
predetermined position with respect to the first electrode. The
polysilicon layer 912 and the metal layer 914 are separated from
each other by a silicon oxide layer 913. The silicon oxide layer
913 is disposed at end parts of the polysilicon layer 912 and metal
layer 914.
[0090] A variable power supply for variably applying a voltage is
connected between the metal layer 911 functioning as the movable
reflecting mirror and acting as the first electrode, and the metal
layer 914 acting as the second electrode. When the voltage applied
between the metal layers 911 and 914 is changed, an electrostatic
force occurs or changes, thereby forming flexure in the metal layer
911 and polysilicon layer 912 at the center part not provided with
the silicon oxide layer 913. As a consequence, the curved surface
form of the reflecting surface deforms, so that individual parts of
the reflecting surface migrate.
[0091] Without being restricted to the above-mentioned embodiments,
the present invention can be modified in various manners. For
example, though the diffraction grating device acting as wavelength
branching means is of transmission type in the above-mentioned
embodiments, it may be of reflection type as well. Instead of the
diffraction grating device, a photonic crystal may be used as the
wavelength branching means. When multiplexed multiwavelength signal
light is inputted, the photonic crystal can output individual
wavelength components of signal light into spatially different
optical paths in response to the respective wavelengths. In this
regard, the photonic crystal exhibits an effect similar to that of
the diffraction grating device. The number of signal light
channels, the number of input/output ports, and the number of
mirrors are not restricted to those explained in the
above-mentioned embodiments.
[0092] As explained in detail in the foregoing, the respective
light input/output directions of a plurality of input/output ports
included in the optical input/output means are located on the first
virtual plane and parallel to each other in the present invention.
The individual wavelength light components outputted from the
wavelength branching means after wavelength separation have
respective optical axes located on the second virtual plane. The
first and second virtual planes are not parallel to each other. The
light fed into the wavelength branching means after being
collimated by the first optical system has a greater beam width in
a direction parallel to the second virtual plane than in a
direction perpendicular to the second virtual plane. Such
characteristic features allow the optical signal processor in
accordance with the present invention to improve its wavelength
resolution and reduce its size.
[0093] From the foregoing explanations of the invention, it will be
obvious that the same may be varied in many ways. Such variations
are not to be regarded as a departure from the spirit and scope of
the invention, and all such modifications as would be obvious to
one skilled in the art are intended to be included within the scope
of the following claims.
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